This grant is a revised version of previous application 1 R03 AG024640-01. The overall goal of this grant application is to examine the role of mitochondria in aging, and, in particular, to test the mitochondrial theory of aging in mouse skeletal muscles. According to this theory, somatic mitochondrial DNA (mtDNA) mutations cause defective electron transfer, increasing the generation of damaging reactive oxygen species (ROS), that, in turn, produce further mtDNA mutations. This vicious cycle presumably results in compromised mitochondrial function including decreased energy production. The ensuing tissue degeneration will lead to various aging phenotypes. There are circumstantial evidences to support this theory, and some specific mtDNA mutations have been reported to accumulate in various tissues during aging. However, there is still no comprehensive study on the overall mtDNA mutation (all kinds of mutations co-exist in the same cell including those with low abundance) accumulation during aging. Perhaps more importantly, the physiological consequences of the aging related mtDNA mutations are largely unclear. We recently developed a novel approach to transfer mtDNA from mouse skeletal muscle to an in vitro cell culture system, and improved methods to isolate and identify mtDNA mutations. Combined with the established technologies, we will investigate the accumulation of overall mtDNA mutations in skeletal muscle during aging by evaluating individual mtDNA from the muscle in young, middle-age and old mice, and further isolate and identify age-associated mtDNA mutations. The success of study will help us to gain insights of molecular mechanism of aging and aging-related human degenerative diseases. [unreadable] [unreadable] [unreadable] [unreadable]